Fuse



Feb. 18, 1936. G. R. BROWN, 2,031,457

FUSE

Filed Feb. 27, 1934 f gs Inventor:

George R. Brown,

b9 15% MM is ttor" hey.

Patented Feb. 18, 1936 PATENT OFFICE FUSE George R. Brown, Bridgeport, Conn., assignor to General Electric Company, a corporation of New York Application February 27, 1934, Serial No. 713,081

3 Claims.

My invention relates to fuses and more particularly to fuses of the plug type. Plug" fuses are generally used to protect the individual circuits of a house wiring system.

Operation of these fuses depends upon the melting of a fuse link to open the circuit. Fuses of low current rating operate quickly on heavy current overloads due to the rapid melting of the relatively small fuse link. On small overloads which are slightly in excess of the rating of the fuse the arc drawn between the severed ends on the melting of the fuse link is unstable and so will not persist for a very long time. Difiiculty has been experienced with fuses of high current rating which may operate quite satisfactorily on relatively heavy overloads as on short circuits. These fuses may fail to operate on the long persistence of the are on overloads that are slightly in excess of the rating of the fuse. The long persistence of the are or the failure of the fuse to operate may result in the are destroying the fuse and then striking between parts of the fuse support. This may result in serious damage to the fuse support ultimately resulting in a fire or may cause damage to the electrical apparatus connected in the circuit.

The object of my invention is to provide a fuse which will operate more certainly and quickly especially when provided with a fuse link having a relatively high current rating.

What I consider to be novel and my invention will be better understood by reference to the following specification and appended claims when considered in connection with the accompanying drawing, in which Fig. l is a side View of my improved fuse with a portion of the metal shell cut away to expose the part beneath; Fig. 2 is a sectional view along the line. 22 of Fig. 1 looking in the direction indicated by the arrows, and Fig. 3 is a sectional view along line 33 of Fig. 1 looking in the direction indicated by the arrows.

In the drawing the plug fuse of my invention is indicated generally by the numeral II) and consists of a base II and a cap I2 both formed of molded insulating material. Cap I2 is provided with a cylindrical extension I3 which overlies a considerable portion of the base II. A center contact I4 is provided for the fuse and is secured in a central opening in the base II. The second contact for the fuse consists of a screw shell I5 which threads on integral screw threads It provided on cap I2, as best indicated in Fig. 1. Screw shell I5 serves to secure base I I and cap I2 together. Radial movement between cap I2 and base II is prevented by the seating of projections H and I8 of base II in corresponding recesses provided in cap I2. A fuse link I9 is provided and connected at one end to center contact I4 and at the other end to screw shell I5. To permit examination of the condition of fuse link I9, a transparent window 20 is secured over an opening provided in cap I2 and is held in position by engagement with the top of base I I. To permit the escape of gases generated on the operation. of the fuse, a space is provided between the side walls of base II and cap I2 and communicates with radial recesses 2| of base II and longitudinal recesses 22 of cap I2. As indicated in Figs. 2 and 3, fuse link I9 rests in one of the recesses 2I and passes up along the side of cap I2 in one of the recesses 22. It is to be noted that fuse link I9 does not fully occupy the space provided by these recesses. The end of cap I2 is spaced from shoulder 23 of base II by the portion of fuse link I 9 which passes over the end out cap I2 and engages projection ll of base II. This provides a communicating passage between recess 22 of cap I2 and the space between the side walls of the base II and cap I2. The insulating material of which the molded cap I2 is made may be damaged by an arc persisting for a considerable length of time within the fuse upon its operation. To protect the side walls of cap I2 from direct contact with the arc and to insure a quick and certain extinction of the are, a metal sleeve 24 is provided substantially covering the inner wall of the extension I3 of cap I2. By the provision of this metal sleeve 24 the metallic vapor generated on volatilization of the fuse link I9 is condensed as it passes out of the fuse through the recesses 2| and 22 provided for its escape. The metal sleeve 24- not only provides a surface of high heat conduction which will condense the metallic vapor but also prevents heat localization on the inner surface of extension I3 which may crack the extension. If extension I3 is injured then the arc may strike directly from the center terminal to the metal parts of the fuse support. An arc may then develop which will do great damage to the fuse support and to the apparatus connected in the circuit. The condensation of this metallic vapor greatly reduces the amount of metal vapor in the arc path and so greatly reduces the length of time which the are will persist. It has been found that the provision of this metal sleeve not only results in the quick operation of the fuse but also assures the operation of the fuse even when a fuse of high current rating is operated by an overload only slightly in excess of the rating of the fuse. This metallic sleeve 24 may be made from a thin sheet of copper formed into a ring of substantially the diameter of the inner wall of extension I3. While copper is preferred, sleeve 24 may be made from any other metal.

From the foregoing, it may be seen that a plug fuse is provided with a metallic sleeve surrounding a portion of the fuse link which assures .a quick operation of the fuse without damage to the fuse and its support or the electrical devices which may be connected in the circultby an undue prolongation of the fault. In addition, the metallic sleeve assures a completed operation of the fuse even though the current may not greatly exceed the rating of the fuse.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric fuse comprising .a basexof insulating material, a cap of insulating material, an extension from saidcap passing over a portion of said base, communicating recesses to permit gases to escape between said extension and said base, a fuse link located within said extension,

and a metal sleeve covering the inner wall of said extension whereby escaping gases may condense on said sleeve.

2. An electric fuse comprising a base of insulating material, a cap of insulating material having an extension passing over a portion of said base, communicating recesses to permit gases to escape between said extension and said base, a center contact secured to said base, a metal shell threaded over said base and cap, a fuse link connected to said center contact and said shell, and a. .metal sleeve covering the inner wall of the extension of said cap whereby escaping metallic vapors may condense on said sleeve.

3. An electric fuse comprising a base of insulating material, a cap of insulating material having anextension passing over a portion of said base, communicating recesses to permit gases to-escape between said extension and said base, a center contact secured to said base, a metal shell threaded over said cap and base, a fuse link connectedto said center contact and said shell, and :a metallic sleeve surrounding a portion of said fuse link whereby escaping metallic vapors may condense on said sleeve.

GEORGE R. BROWN. 

